A “speaker” generates sound from an electrical signal. In the hearing aid art, one often encounters the term “receiver” for such a device, which reads strangely to the uninitiated. “Electroacoustic transducer” is clumsy and pedantic. Thus, “speaker” is the term used for describing this invention.
A human ear canal is a narrow, irregular, tubular structure, approximately 25 mm in length. Coupling amplified sound to the eardrum at the inner end of the canal is not as simple as it might seem. In a hearing aid, a microphone is connected to a speaker by a high gain (60-80 dB) amplifier and is relatively close to the speaker. An earpiece containing a speaker is assumed to fit the ear canal and the tissue of the ear canal is relied upon to isolate the speaker from the microphone.
If the earpiece should move slightly and not seal the ear canal, an acoustic path is opened, coupling the speaker to the microphone, which permits sound from the speaker to be fed back to the microphone. Feedback typically occurs at high frequencies due to the higher gain at these frequencies, where most hearing loss occurs. The misalignment of the earpiece manifests itself as an unpleasant squeal that can be audible even to those several feet from the hearing aid. The squeal can be eliminated by reducing the gain of the amplifier by way of a volume control on the hearing aid. Often the wearer is obliged to adjust the gain frequently as the loudness of background sounds and the loudness of sounds of interest change. Feedback in a hearing aid can interfere with hearing and may cause the wearer not to use the hearing aid. High level feedback in a hearing aid may even damage the already impaired hearing of the wearer.
Hearing aids can be divided into four groups: Behind-The-Ear (BTE), In-The-Ear (ITE), In-The-canal (ITC), and Completely-In-the-Canal (CIC). Some BTE hearing aids have an advantage over other types because the speaker is relatively far from any microphone in the body of the hearing aid. Before speakers became small enough to fit in an ear canal, it was known to add sound absorbing material to the earpiece of a BTE hearing aid; for example see U.S. Pat. No. 3,080,011. It has long been known that putting the speaker in the ear canal reduces feedback in a BTE hearing aid. See “Reducing Feedback in a Post-Auricular Hearing Aid by Implanting the Receiver in an Earmold”, Ross and Cirmo, The Volta Reuiew, January 1980, pages 40-44. (Post auricular means behind the ear). See also U.S. Pat. No. 4,727,582 (de Vries et al.). Distance and dispersion provide some attenuation but, for those severely impaired, these are not enough. The high gain used for at least some frequencies assures that sufficient sound reaches a microphone for oscillation or squeal.
A tip having a foam sleeve or jacket is known in the art and can be used with any type hearing aid but is primarily used with BTE hearing aids. The tip contains a speaker. The sleeve provides a resilient coupling to the wall of the ear canal and provides some attenuation of the sound traveling in either direction along the canal.
It is known in the art to form the sleeve in the canal and it is known to pre-form the sleeve. In some cases, the sleeve is designed for comfort; e.g. U.S. Pat. No. 4,880,076 (Ahlberg et al.). It is alleged for other sleeves that feedback is prevented; e.g. U.S. Pat. No. 4,830,139 (Cirillo) and U.S. Pat. No. 6,724,902 (Shennib et al.). It is known in the art to make a sleeve from foam; e.g. U.S. Pat. No. 4,459,247 (Rothemund). Despite these disclosures, there remains a need in the art for a jacketed tip that is comfortable to wear and that prevents feedback even at high gain. That is, there is a need for a jacketed tip that attenuates sound a minimum of 40 dB and preferably 60 dB, particularly at and above 1,000 Hz.
In view of the foregoing, it is therefore an object of the invention to provide a jacketed tip for a hearing aid that provides at least 40-60 dB of attenuation and is comfortable to wear.
Another object of the invention is to provide a jacketed tip for a hearing aid that provides at least 40 dB of attenuation even at low frequencies
A further object of the invention is to provide a pre-formed, high attenuation sleeve for a hearing aid.
Another object of the invention is to provide a high gain, BTE hearing aid with a speaker in the ear canal surrounded by sound absorbing, resilient material.